Despite the fact that youth involved in the child welfare (CW) and runaway and homeless youth (RHY) systems are particularly vulnerable to being trafficked, there is no consensus screening tool to identify trafficking experiences among such youth. In order to better serve youth trafficking victims, a Human Trafficking Screening Tool (HTST), along with a Short Form version (HTST-SF), was developed and pretested with 617 RHY- and CW-involved youth, ages 12 to 24, across 14 RHY and CW settings in New York, Texas, and Wisconsin in 2016. The survey captured their trafficking experiences as well as demographic characteristics and other life experiences related to trafficking (e.g., running away, drug abuse). Overall, the HTST and HTST-SF performed equally well at capturing trafficking experiences for most youth. Practitioners assessed the tool as easy to administer and the youths responses as truthful and indicating understanding of the questions. Responses to the HTST were correlated to known trafficking risk factors and outcomes, including running away from home, being kicked out of ones home, abusing prescription or over-the-counter drugs, trading sex for something of value on their own, being arrested, and seeking help. In addition, the HTST correctly predicted trafficking victimization. Additional testing of youth under age 18 and youth in CW settings, in addition to further validation work with a nationally representative sample of youth, is recommended. (Author Abstract Modified)